1. Field of the Invention
This invention relates to an alternative light emitting device, which gives no feeling of strangeness for users, to a conventional halogen lamp. The light emitting device comprises: a surface light source; a lens provided in front of the surface light source and receiving light from the surface light source; and a reflector accommodating the surface light source and the lens, and reflecting the light diverging from the lends. And a relation between a light emitting area of the surface light source and a light receiving area of the lens is properly designed.
2. Description of the Related Art
A light-emitting diode “LED”, which has good points such as low power consumption and long life as against a conventional halogen lamp, is widely used, because people become more ecology conscious. And people consider that using the LED is one policy for the energy-saving strategies. Particularly, it is highly required to use the LED as an alternate item of the halogen lamp or the like.
But there is a problem that the light from the LED provides a feeling of strangeness for users accustomed to the conventional halogen lamps. In general, the light from a LED has a directional pattern, a lambertian pattern. Using the LED as a replacement for the halogen lamp causes a large difference in intensity between a strong light illuminating the center and near the center of illumination and a weak light illuminating a circumference of them. “The center of illumination” is an intersection point of an illuminated surface and a light axis of the light emitting device.
One method for reducing the feeling of strangeness has been studied. The method uses a surface light source, an electro-luminescence or the like to enlarging the area illuminated by the strong light. The surface light source has a lot of LED elements arranged a base plate. Furthermore, a light emitting device increasing a uniformity of the strong light by increasing a light condensing efficiency has been developed (e.g., Patent document 1: Japanese Laid-Open Patent Publication No. 2007-235079). The light emitting device has a CPC (Compound Parabolic Concentrators) lens combined with the surface light source.
As shown in FIG. 3, the CPC lens 1 is a bullet-shaped cylinder having a side reflective surface 2 determined by a trajectory made by rotating a pair of parabolas A, B around a rotating center CL. The parabolas A, B are axisymmetrically-arranged by the rotating center CL, and each focal point of the parabolas A, B has different position each other. Furthermore, the CPC lens has a light receiving surface 3 and a light emitting surface 4, which are in a direction perpendicular to the rotating center CL. In the Patent document 1, the cylindrical CPC lens 1 is disclosed. A solid transparent cylinder having the same shaped side reflective surface 2 performs the same function. Light entering this CPC lens 1 through the light receiving surface 3 is emitted from the light emitting surface 4 in the range of an aperture angle θ centering the rotating center CL. The rotating center CL is a light axis of the CPC lens 1.
The uniformity of the light illuminating the illuminated surface is increased by using such a CPC lens, because the light entering into the CPC lens 1 through the light receiving surface 3 is emitted from the light emitting surface 4 within an aperture angle θ. The light emitting device further reduces the feeling of strangeness of the users than a case using the surface light source alone.